Pressure-sensitive adhesives (PSA) are well known and are used for a variety of industrial, consumer and medical applications. Pressure-sensitive adhesives are characterized as being normally tacky and exhibiting instant tack when applied to a substrate. A variety of polymers have been used to manufacture PSA, for example, acrylic and methacrylic ester homo- or copolymers, butyl rubber-based systems, silicones, urethanes, vinyl esters and amides, olefin copolymer materials, natural or synthetic rubbers, and the like.
Typically, the bond strength of a PSA remains the same or increases with time after application to a substrate. Increased bond strength may result from increased polymer flow or improved wetting over a period of time, or it may result from hydrogen bonding to a polar substrate or from covalent or ionic chemical interactions. Removal of an adhesive after application to a substrate is often desirable. For example, tape may be applied to a substrate to mask off a portion during a painting operation, at the completion of which the tape must be removed. Wallpaper can be applied with a PSA and removal at a future date is usually desirable. Adhesives applied to human skin, for example on a bandaid, wound dressing, transdermal drug delivery device, or monitoring or stimulating electrode, must be removed at a later date. In all of these instances and many others, it is desirable to be able to readily remove the adhesive without the need for harsh chemicals or special equipment.
The ideal performance characteristics of an adhesive intended for use on human skin, specifically, present difficult and conflicting technical requirements. The ideal medical adhesive should, first of all, be nonirritating yet bond quickly to skin at the intended site of use. At the same time, clearly, it should not stick to other objects until it is actually applied to the target site. The adhesive should maintain its bond for as long a period of time as necessary and be resistant to inadvertent removal. Furthermore, the adhesive should not be weakened or destroyed by exposure to moisture or high humidity. Finally, in order to provide protection to a wound or to maintain the integrity of placement of an electrode or other device the adhesive should resist skin movement and be able to transfer a mechanical load from the adhesive backing to the skin.
The present invention is directed to adhesive assemblies formulated with such an adhesive composition. The composition is substantially non-tacky at room temperature and tacky at skin temperature. In one embodiment, adhesion is "temperature reversible". That is, adhesive articles may be formulated so as to stick aggressively to the skin but can nevertheless be readily removed therefrom with near-zero peel strength by simple chilling.